REVERSIBLE MIGRATION OF LITHIUM IN MONTMORILLONITES

The migration of lithium cations into the lattice of dioctahedral clay s upon heating, considered up to now as irreversible, has been investi gated. The samples under examination are two lithium-saturated montmor illonites, selected with different charge-deficit distributions betwee n the tetrahedral and octahedral sheets, to obtain direct information on the structural changes occurring in both layers. Reexpansion of the se samples previously collapsed at 300 degrees C has been attained, fo r the first time, under high vapor water pressures. A structural chara cterization of the smectites under the different treatments has been m onitored by means of X-ray diffraction, XRD, Fourier transform infrare d spectroscopy, FTIR, and Si-29, Al-27, and Li-7 magic angle spinning nuclear magnetic resonance, MAS-NMR. The effect that Li+ ions exert on the quadrupolar coupling constant of tetrahedral Al ions has been sho wn. Direct experimental evidence on the location of lithium ions in th e hexagonal holes of the collapsed structure is provided. Additionally , generation of protons during the rehydration process is concluded.